<?php
/**
 * Class used internally by Diff to actually compute the diffs.  This class is
 * implemented using native PHP code.
 *
 * The algorithm used here is mostly lifted from the perl module
 * Algorithm::Diff (version 1.06) by Ned Konz, which is available at:
 * http://www.perl.com/CPAN/authors/id/N/NE/NEDKONZ/Algorithm-Diff-1.06.zip
 *
 * More ideas are taken from:
 * http://www.ics.uci.edu/~eppstein/161/960229.html
 *
 * Some ideas (and a bit of code) are taken from analyze.c, of GNU
 * diffutils-2.7, which can be found at:
 * ftp://gnudist.gnu.org/pub/gnu/diffutils/diffutils-2.7.tar.gz
 *
 * Some ideas (subdivision by NCHUNKS > 2, and some optimizations) are from
 * Geoffrey T. Dairiki <dairiki@dairiki.org>. The original PHP version of this
 * code was written by him, and is used/adapted with his permission.
 *
 * $Horde: framework/Text_Diff/Diff/Engine/native.php,v 1.3 2006/01/06 15:56:52 jan Exp $
 *
 * @author  Geoffrey T. Dairiki <dairiki@dairiki.org>
 * @package Text_Diff
 *
 * @access private
 */
class Text_Diff_Engine_native {

		function diff($from_lines, $to_lines)
		{
				array_walk($from_lines, array('Text_Diff', 'trimNewlines'));
				array_walk($to_lines, array('Text_Diff', 'trimNewlines'));

				$n_from = count($from_lines);
				$n_to = count($to_lines);

				$this->xchanged = $this->ychanged = array();
				$this->xv = $this->yv = array();
				$this->xind = $this->yind = array();
				unset($this->seq);
				unset($this->in_seq);
				unset($this->lcs);

				// Skip leading common lines.
				for ($skip = 0; $skip < $n_from && $skip < $n_to; $skip++) {
						if ($from_lines[$skip] !== $to_lines[$skip]) {
								break;
						}
						$this->xchanged[$skip] = $this->ychanged[$skip] = false;
				}

				// Skip trailing common lines.
				$xi = $n_from; $yi = $n_to;
				for ($endskip = 0; --$xi > $skip && --$yi > $skip; $endskip++) {
						if ($from_lines[$xi] !== $to_lines[$yi]) {
								break;
						}
						$this->xchanged[$xi] = $this->ychanged[$yi] = false;
				}

				// Ignore lines which do not exist in both files.
				for ($xi = $skip; $xi < $n_from - $endskip; $xi++) {
						$xhash[$from_lines[$xi]] = 1;
				}
				for ($yi = $skip; $yi < $n_to - $endskip; $yi++) {
						$line = $to_lines[$yi];
						if (($this->ychanged[$yi] = empty($xhash[$line]))) {
								continue;
						}
						$yhash[$line] = 1;
						$this->yv[] = $line;
						$this->yind[] = $yi;
				}
				for ($xi = $skip; $xi < $n_from - $endskip; $xi++) {
						$line = $from_lines[$xi];
						if (($this->xchanged[$xi] = empty($yhash[$line]))) {
								continue;
						}
						$this->xv[] = $line;
						$this->xind[] = $xi;
				}

				// Find the LCS.
				$this->_compareseq(0, count($this->xv), 0, count($this->yv));

				// Merge edits when possible.
				$this->_shiftBoundaries($from_lines, $this->xchanged, $this->ychanged);
				$this->_shiftBoundaries($to_lines, $this->ychanged, $this->xchanged);

				// Compute the edit operations.
				$edits = array();
				$xi = $yi = 0;
				while ($xi < $n_from || $yi < $n_to) {
						assert($yi < $n_to || $this->xchanged[$xi]);
						assert($xi < $n_from || $this->ychanged[$yi]);

						// Skip matching "snake".
						$copy = array();
						while ($xi < $n_from && $yi < $n_to
 									&& !$this->xchanged[$xi] && !$this->ychanged[$yi]) {
								$copy[] = $from_lines[$xi++];
								++$yi;
						}
						if ($copy) {
								$edits[] = &new Text_Diff_Op_copy($copy);
						}

						// Find deletes & adds.
						$delete = array();
						while ($xi < $n_from && $this->xchanged[$xi]) {
								$delete[] = $from_lines[$xi++];
						}

						$add = array();
						while ($yi < $n_to && $this->ychanged[$yi]) {
								$add[] = $to_lines[$yi++];
						}

						if ($delete && $add) {
								$edits[] = &new Text_Diff_Op_change($delete, $add);
						} elseif ($delete) {
								$edits[] = &new Text_Diff_Op_delete($delete);
						} elseif ($add) {
								$edits[] = &new Text_Diff_Op_add($add);
						}
				}

				return $edits;
		}

		/**
 		* Divides the Largest Common Subsequence (LCS) of the sequences (XOFF,
 		* XLIM) and (YOFF, YLIM) into NCHUNKS approximately equally sized
 		* segments.
 		*
 		* Returns (LCS, PTS).  LCS is the length of the LCS. PTS is an array of
 		* NCHUNKS+1 (X, Y) indexes giving the diving points between sub
 		* sequences.  The first sub-sequence is contained in (X0, X1), (Y0, Y1),
 		* the second in (X1, X2), (Y1, Y2) and so on.  Note that (X0, Y0) ==
 		* (XOFF, YOFF) and (X[NCHUNKS], Y[NCHUNKS]) == (XLIM, YLIM).
 		*
 		* This function assumes that the first lines of the specified portions of
 		* the two files do not match, and likewise that the last lines do not
 		* match.  The caller must trim matching lines from the beginning and end
 		* of the portions it is going to specify.
 		*/
		function _diag ($xoff, $xlim, $yoff, $ylim, $nchunks)
		{
				$flip = false;

				if ($xlim - $xoff > $ylim - $yoff) {
						/* Things seems faster (I'm not sure I understand why) when the
 						* shortest sequence is in X. */
						$flip = true;
						list ($xoff, $xlim, $yoff, $ylim)
								= array($yoff, $ylim, $xoff, $xlim);
				}

				if ($flip) {
						for ($i = $ylim - 1; $i >= $yoff; $i--) {
								$ymatches[$this->xv[$i]][] = $i;
						}
				} else {
						for ($i = $ylim - 1; $i >= $yoff; $i--) {
								$ymatches[$this->yv[$i]][] = $i;
						}
				}

				$this->lcs = 0;
				$this->seq[0]= $yoff - 1;
				$this->in_seq = array();
				$ymids[0] = array();

				$numer = $xlim - $xoff + $nchunks - 1;
				$x = $xoff;
				for ($chunk = 0; $chunk < $nchunks; $chunk++) {
						if ($chunk > 0) {
								for ($i = 0; $i <= $this->lcs; $i++) {
										$ymids[$i][$chunk - 1] = $this->seq[$i];
								}
						}

						$x1 = $xoff + (int)(($numer + ($xlim-$xoff)*$chunk) / $nchunks);
						for (; $x < $x1; $x++) {
								$line = $flip ? $this->yv[$x] : $this->xv[$x];
								if (empty($ymatches[$line])) {
										continue;
								}
								$matches = $ymatches[$line];
								foreach ($matches as $y) {
										if (empty($this->in_seq[$y])) {
												$k = $this->_lcsPos($y);
												assert($k > 0);
												$ymids[$k] = $ymids[$k - 1];
												break;
										}
								}

								while (list($junk, $y) = each($matches)) {
										if ($y > $this->seq[$k - 1]) {
												assert($y < $this->seq[$k]);
												/* Optimization: this is a common case: next match is
 												* just replacing previous match. */
												$this->in_seq[$this->seq[$k]] = false;
												$this->seq[$k] = $y;
												$this->in_seq[$y] = 1;
										} elseif (empty($this->in_seq[$y])) {
												$k = $this->_lcsPos($y);
												assert($k > 0);
												$ymids[$k] = $ymids[$k - 1];
										}
								}
						}
				}

				$seps[] = $flip ? array($yoff, $xoff) : array($xoff, $yoff);
				$ymid = $ymids[$this->lcs];
				for ($n = 0; $n < $nchunks - 1; $n++) {
						$x1 = $xoff + (int)(($numer + ($xlim - $xoff) * $n) / $nchunks);
						$y1 = $ymid[$n] + 1;
						$seps[] = $flip ? array($y1, $x1) : array($x1, $y1);
				}
				$seps[] = $flip ? array($ylim, $xlim) : array($xlim, $ylim);

				return array($this->lcs, $seps);
		}

		function _lcsPos($ypos)
		{
				$end = $this->lcs;
				if ($end == 0 || $ypos > $this->seq[$end]) {
						$this->seq[++$this->lcs] = $ypos;
						$this->in_seq[$ypos] = 1;
						return $this->lcs;
				}

				$beg = 1;
				while ($beg < $end) {
						$mid = (int)(($beg + $end) / 2);
						if ($ypos > $this->seq[$mid]) {
								$beg = $mid + 1;
						} else {
								$end = $mid;
						}
				}

				assert($ypos != $this->seq[$end]);

				$this->in_seq[$this->seq[$end]] = false;
				$this->seq[$end] = $ypos;
				$this->in_seq[$ypos] = 1;
				return $end;
		}

		/**
 		* Finds LCS of two sequences.
 		*
 		* The results are recorded in the vectors $this->{x,y}changed[], by
 		* storing a 1 in the element for each line that is an insertion or
 		* deletion (ie. is not in the LCS).
 		*
 		* The subsequence of file 0 is (XOFF, XLIM) and likewise for file 1.
 		*
 		* Note that XLIM, YLIM are exclusive bounds.  All line numbers are
 		* origin-0 and discarded lines are not counted.
 		*/
		function _compareseq ($xoff, $xlim, $yoff, $ylim)
		{
				/* Slide down the bottom initial diagonal. */
				while ($xoff < $xlim && $yoff < $ylim
 							&& $this->xv[$xoff] == $this->yv[$yoff]) {
						++$xoff;
						++$yoff;
				}

				/* Slide up the top initial diagonal. */
				while ($xlim > $xoff && $ylim > $yoff
 							&& $this->xv[$xlim - 1] == $this->yv[$ylim - 1]) {
						--$xlim;
						--$ylim;
				}

				if ($xoff == $xlim || $yoff == $ylim) {
						$lcs = 0;
				} else {
						/* This is ad hoc but seems to work well.  $nchunks =
 						* sqrt(min($xlim - $xoff, $ylim - $yoff) / 2.5); $nchunks =
 						* max(2,min(8,(int)$nchunks)); */
						$nchunks = min(7, $xlim - $xoff, $ylim - $yoff) + 1;
						list($lcs, $seps)
								= $this->_diag($xoff, $xlim, $yoff, $ylim, $nchunks);
				}

				if ($lcs == 0) {
						/* X and Y sequences have no common subsequence: mark all
 						* changed. */
						while ($yoff < $ylim) {
								$this->ychanged[$this->yind[$yoff++]] = 1;
						}
						while ($xoff < $xlim) {
								$this->xchanged[$this->xind[$xoff++]] = 1;
						}
				} else {
						/* Use the partitions to split this problem into subproblems. */
						reset($seps);
						$pt1 = $seps[0];
						while ($pt2 = next($seps)) {
								$this->_compareseq ($pt1[0], $pt2[0], $pt1[1], $pt2[1]);
								$pt1 = $pt2;
						}
				}
		}

		/**
 		* Adjusts inserts/deletes of identical lines to join changes as much as
 		* possible.
 		*
 		* We do something when a run of changed lines include a line at one end
 		* and has an excluded, identical line at the other.  We are free to
 		* choose which identical line is included.  `compareseq' usually chooses
 		* the one at the beginning, but usually it is cleaner to consider the
 		* following identical line to be the "change".
 		*
 		* This is extracted verbatim from analyze.c (GNU diffutils-2.7).
 		*/
		function _shiftBoundaries($lines, &$changed, $other_changed)
		{
				$i = 0;
				$j = 0;

				assert('count($lines) == count($changed)');
				$len = count($lines);
				$other_len = count($other_changed);

				while (1) {
						/* Scan forward to find the beginning of another run of
 						* changes. Also keep track of the corresponding point in the
 						* other file.
 						*
 						* Throughout this code, $i and $j are adjusted together so that
 						* the first $i elements of $changed and the first $j elements of
 						* $other_changed both contain the same number of zeros (unchanged
 						* lines).
 						*
 						* Furthermore, $j is always kept so that $j == $other_len or
 						* $other_changed[$j] == false. */
						while ($j < $other_len && $other_changed[$j]) {
								$j++;
						}

						while ($i < $len && ! $changed[$i]) {
								assert('$j < $other_len && ! $other_changed[$j]');
								$i++; $j++;
								while ($j < $other_len && $other_changed[$j]) {
										$j++;
								}
						}

						if ($i == $len) {
								break;
						}

						$start = $i;

						/* Find the end of this run of changes. */
						while (++$i < $len && $changed[$i]) {
								continue;
						}

						do {
								/* Record the length of this run of changes, so that we can
 								* later determine whether the run has grown. */
								$runlength = $i - $start;

								/* Move the changed region back, so long as the previous
 								* unchanged line matches the last changed one.  This merges
 								* with previous changed regions. */
								while ($start > 0 && $lines[$start - 1] == $lines[$i - 1]) {
										$changed[--$start] = 1;
										$changed[--$i] = false;
										while ($start > 0 && $changed[$start - 1]) {
												$start--;
										}
										assert('$j > 0');
										while ($other_changed[--$j]) {
												continue;
										}
										assert('$j >= 0 && !$other_changed[$j]');
								}

								/* Set CORRESPONDING to the end of the changed run, at the
 								* last point where it corresponds to a changed run in the
 								* other file. CORRESPONDING == LEN means no such point has
 								* been found. */
								$corresponding = $j < $other_len ? $i : $len;

								/* Move the changed region forward, so long as the first
 								* changed line matches the following unchanged one.  This
 								* merges with following changed regions.  Do this second, so
 								* that if there are no merges, the changed region is moved
 								* forward as far as possible. */
								while ($i < $len && $lines[$start] == $lines[$i]) {
										$changed[$start++] = false;
										$changed[$i++] = 1;
										while ($i < $len && $changed[$i]) {
												$i++;
										}

										assert('$j < $other_len && ! $other_changed[$j]');
										$j++;
										if ($j < $other_len && $other_changed[$j]) {
												$corresponding = $i;
												while ($j < $other_len && $other_changed[$j]) {
														$j++;
												}
										}
								}
						} while ($runlength != $i - $start);

						/* If possible, move the fully-merged run of changes back to a
 						* corresponding run in the other file. */
						while ($corresponding < $i) {
								$changed[--$start] = 1;
								$changed[--$i] = 0;
								assert('$j > 0');
								while ($other_changed[--$j]) {
										continue;
								}
								assert('$j >= 0 && !$other_changed[$j]');
						}
				}
		}

}
